[sdiy] A Frequency Standard for Poor People?

[Magnus Danielson]

From: Grant Richter <grichter at asapnet.net>
Subject: Re: [sdiy] A Frequency Standard for Poor People?
Date: Mon, 15 Dec 2003 10:30:09 -0600
Message-ID: <BC033DB1.27E%grichter at asapnet.net>

> on 12/15/03 8:49 AM, Magnus Danielson at cfmd at bredband.net wrote:
> 
> >> signals derived from color television broadcasts
> > 
> > Can be tricky if you are not sure about the traceability of the signal, i.e.
> > if you know that it actually derives from a stable enought source. Both PAL
> > and NTSC allow for single digit PPM deviations and speed of deviations can be
> > quite severe.
> 
> Broadcast network channels (ABC, CBS, NBC) are NIST locked. This is so an
> affiliate signal from each coast is only phase shifted and can be resynched
> with just a delay line. Dates to before digital time base correctors.

My point is that you have to ensure that this is true. Also, by the current
shifts in how TV broadcasting is done, it is not sure that the color-burst is
as good reference as it used to be. I could bore you with the details and give
away alot on all the forms of flaws modern broadcasting and the defect ways to
transport it....

> All the frequencies in video are multiples of 60 Hz in US

Ehum! 60 / 1.001 Hz if I may... this makes a HUGE difference and that very
quickly I might add! Maybe I should even say 30 / 1.001 Hz to be correct, since
that is the frame frequency while the 60 / 1.001 Hz is the field frequency.

> and 50 Hz in Europe.

... and again, 25 Hz for frame frequency.

> This is so "hum bars" (power supply noise) are stable. If you see a
> "hum bar" drifting slowly, it means the broadcast source is reference
> locked.

Actually, this is the reason why the US runs at 30 / 1.001 so that the color
material does not lies on overtones of the powerlines. The NTSC is extra
sensitive to phase shifts as compared to PAL. In PAL a certain off-frequency
aspect is also done, but not as drastic and in the end it works well.

Cheers,
Magnus - with a finger in the video jam pot - too...